Annular barrier

ABSTRACT

The present invention relates to an annular barrier for providing zonal isolation within a tubular structure or a borehole and for sealing off a first zone from a second zone, comprising a tubular metal part configured to be mounted as part of a well tubular metal structure, the tubular metal part having an outer face, an opening and an axial direction along the well tubular metal structure, a first expandable metal sleeve surrounding the tubular metal part and having a first end connected with the outer face of the tubular metal part and a second end, a second expandable metal sleeve surrounding the tubular metal part and having a first end connected with the outer face of the tubular metal part and a second end, wherein the first expandable metal sleeve and the second expandable metal sleeve each has an end section at the second end, the end section of the first expandable metal sleeve is at least partly overlapping the end section of the second expandable metal sleeve along the axial direction creating an overlapping area, the end sections are configured to slide in relation to each other, the first expandable metal sleeve and the second expandable metal sleeve define an annular space together with the tubular metal part, the first expandable metal sleeve extends from the second end of the first expandable metal sleeve away from the overlapping area in a first direction along the axial direction, and the second expandable metal sleeve extends from the second end of the second expandable metal sleeve away from the overlapping area in a second direction opposite the first direction.

The present invention relates to an annular barrier for providing zonal isolation within a tubular structure or a borehole and for sealing off a first zone from a second zone, comprising a tubular metal part configured to be mounted as part of a well tubular metal structure, the tubular metal part having an outer face, an opening and an axial direction along the well tubular metal structure, a first expandable metal sleeve surrounding the tubular metal part and having a first end connected with the outer face of the tubular metal part and a second end, and a second expandable metal sleeve surrounding the tubular metal part and having a first end connected with the outer face of the tubular metal part and a second end.

Known annular barriers are limited by material properties in how much they are capable of expanding radially outwards, and many attempts have been made to optimise the materials and the design of the annular barriers so that the annular barriers are able to expand more radially outwards.

It is an object of the present invention to wholly or partly overcome the above disadvantages and drawbacks of the prior art. More specifically, it is an object to provide an improved annular barrier which is able to be expanded more radially outwards than known annular barriers without decreasing the collapse rating or similar properties.

The above objects, together with numerous other objects, advantages and features, which will become evident from the below description, are accomplished by a solution in accordance with the present invention by an annular barrier for providing zonal isolation within a tubular structure or a borehole and for sealing off a first zone from a second zone, comprising:

-   -   a tubular metal part configured to be mounted as part of a well         tubular metal structure, the tubular metal part having an outer         face, an opening and an axial direction along the well tubular         metal structure,     -   a first expandable metal sleeve surrounding the tubular metal         part and having a first end connected with the outer face of the         tubular metal part and a second end,     -   a second expandable metal sleeve surrounding the tubular metal         part and having a first end connected with the outer face of the         tubular metal part and a second end, and     -   an annular space between the tubular metal part and the         expandable metal sleeves,         wherein the first expandable metal sleeve and the second         expandable metal sleeve each have an end section at the second         end, the end section of the first expandable metal sleeve and         the end section of the second expandable metal sleeve are at         least partly overlapping along the axial direction creating an         overlapping area, the end sections are configured to slide in         relation to each other, the first expandable metal sleeve         extends from the second end of the first expandable metal sleeve         away from the overlapping area in a first direction along the         axial direction and the second expandable metal sleeve extends         from the second end of the second expandable metal sleeve away         from the overlapping area in a second direction opposite the         first direction.

By having an annular barrier having two expandable and overlapping metal sleeves, an annular barrier having a larger radial expansion than known annular barriers is obtained.

Moreover, the end sections of the overlapping area may be unconnected to the outer face of the tubular metal part.

Also, the annular barrier may comprise a third expandable metal sleeve surrounding the tubular metal part and having a first end connected with the outer face of the tubular metal part and a second end, an end section of the first end of the second expandable metal sleeve and an end section of the second end of the third expandable metal sleeve are at least partly overlapping along the axial direction creating a second overlapping area so that the second expandable metal sleeve is arranged intermediate and partly overlapping the first and second expandable metal sleeves. Furthermore, the overlapping area may be without connection to the outer face of the tubular metal part.

Additionally, the annular space may be fluidly connected with the opening.

Also, the material of the expandable metal sleeves in the overlapping area may be less ductile than the rest of the expandable metal sleeves.

Furthermore, the end sections of the overlapping area may have a greater common thickness than the rest of the expandable metal sleeves.

In addition, at least one sealing element may be arranged between the end sections of the overlapping area(s).

Moreover, at least one sealing element may be arranged in a groove in one of the end sections of the expandable metal sleeves.

Further, the end section of the first expandable metal sleeve may be arranged sliding along an outer face of the second expandable metal sleeve, the end of the second sleeve provides a piston effect during expansion providing a pressure in the axial direction to the end of the second expandable metal sleeve.

Also, the end section of the second end of the second expandable metal sleeve may be arranged sliding along an inner face of the first expandable metal sleeve and the end section of the first end of the second expandable metal sleeve may be arranged sliding along an inner face of the third expandable metal sleeve.

Moreover, the second expandable metal sleeve may have a varying thickness.

Furthermore, the second expandable metal sleeve may have an intermediate section in between the first and second ends which intermediate section may have a thickness being less than the thickness at the first and second ends.

In addition, the second expandable metal sleeve may have a curved cross-section along the axil extension of the annular barrier.

Additionally, the overlapping area(s) may remain substantially unexpanded during expansion of the rest of the expandable metal sleeve.

Also, each expandable metal sleeve may be constituted by a first section and a second section, the second section is the end section and the first section is the rest of the expandable metal sleeve.

Furthermore, the first section may have an unexpanded condition and an expanded condition, the first section is capable of expanding more than 30% than in the unexpanded condition.

The end section of each sleeve may have a length of at least 5% of a total length of the expandable metal sleeve in the unexpanded condition.

In addition, the end section of the first expandable metal sleeve may have grooves which correspond to grooves on the outer face of the end section of the second expandable metal sleeve forming a ratchet system hindering the end section of the first expandable metal sleeve from returning once moved away from the end section of the second expandable metal sleeve.

The annular barrier according to the present invention may further comprise a shear pin assembly fluidly connecting the expansion opening and the annular space in order to allow expansion fluid within the well tubular structure to expand the expandable sleeve.

Moreover, the shear pin assembly may have a first position in which expansion fluid is allowed to flow into the annular space and a second position in which the expansion opening is blocked, preventing expansion fluid from entering the annular space.

In addition, fluid from an inside of the tubular metal part may enter the expansion unit via the opening and further into the annular space.

The annular barrier according to the present invention may further comprise an anti-collapsing unit comprising an element movable at least between a first position and a second position, the anti-collapsing unit having a first inlet which is in fluid communication with the first zone, and a second inlet which is in fluid communication with the second zone, and the anti-collapsing unit having an outlet which is in fluid communication with the annular space, and in the first position, the first inlet is in fluid communication with the outlet, equalising the first pressure of the first zone with the space pressure, and in the second position, the second inlet is in fluid communication with the outlet, equalising the second pressure of the second zone with the space pressure.

The anti-collapse unit may be fluidly connected to the opening or the expansion unit.

The annular barrier according to the present invention may further comprise sealing elements arranged on an outer face of the expandable metal sleeves.

Also, the sealing elements may be arranged in grooves on an outer face of the expandable metal sleeves.

Also, a sealing element and a split ring-shaped retaining element may be arranged in a groove, the split ring-shaped retaining element forming a back-up for the sealing element.

Additionally, the split ring-shaped retaining element may have more than one winding so that when the expandable tubular is expanded from a first outer diameter to a second outer diameter being larger than the first outer diameter, the split ring-shaped retaining element partly unwinds.

Furthermore, an intermediate element may be arranged between the split ring-shaped retaining element and the sealing element.

Moreover, the first ends of the expandable metal sleeves may be welded to the outer face of the tubular metal part.

Finally, the annular barrier according to the present invention may further comprise a first connection part connecting the first end of the first expandable metal sleeve to the outer face of the tubular metal part and a second connection part connecting the first end of the second expandable metal sleeve to the outer face of the tubular metal part.

The invention and its many advantages will be described in more detail below with reference to the accompanying schematic drawings, which for the purpose of illustration show some non-limiting embodiments and in which:

FIG. 1A shows a cross-sectional view of an annular barrier in its unexpanded condition,

FIG. 1B shows a cross-sectional view of the annular barrier of FIG. 1A in its expanded condition isolating the first zone from the second zone,

FIG. 2A shows a cross-sectional view of another annular barrier in its unexpanded condition,

FIG. 2B shows a cross-sectional view of the annular barrier of FIG. 2B in its partly expanded and intermediate condition during expansion,

FIG. 2C shows a cross-sectional view of the annular barrier of FIG. 2B in its expanded condition,

FIG. 3 shows a cross-sectional view of another annular barrier in its unexpanded condition,

FIG. 4 shows in perspective part of another annular barrier having a shear pin assembly and an anti-collapsing unit,

FIGS. 5A and 5B show a cross-sectional view of part of another annular barrier having a shear pin assembly, the shear pin assembly is shown in a first position in FIG. 5A and in its second closed position in FIG. 5B,

FIG. 6 shows a cross-sectional view of an anti-collapse unit,

FIG. 7 shows a cross-sectional view of another annular barrier in its unexpanded condition, and

FIG. 8 shows a cross-sectional view of yet another annular barrier in its unexpanded condition.

All the figures are highly schematic and not necessarily to scale, and they show only those parts which are necessary in order to elucidate the invention, other parts being omitted or merely suggested.

FIG. 1A shows an annular barrier 1 for providing zonal isolation within a borehole 2 and for sealing off a first zone 101 from a second zone 101, as shown in FIG. 1B. The annular barrier comprises a tubular metal part 7 configured to be mounted as part of a well tubular metal structure 3. The tubular metal part 7 has an outer face 4 and at least one opening 16 through which fluid may pass to expand the annular barrier. The tubular metal part has an axial direction L substantially coincident with the well tubular metal structure. The annular barrier further comprises a first expandable metal sleeve 6 surrounding the tubular metal part and having two ends i.e. a first end 9 connected with the outer face of the tubular metal part and a second end 10. The annular barrier 1 further comprises a second expandable metal sleeve 8 surrounding the tubular metal part 7 and having a first end 12 connected with the outer face 4 of the tubular metal part and a second end 14. The first expandable metal sleeve 6 has an end section 21, 21A at its second end 10 and the second expandable metal sleeve 8 has an end section 21, 21B at its second end 14. The end section 21, 21A of the first expandable metal sleeve and the end section 21, 21B of the second expandable metal sleeve are partly overlapping along the axial direction creating an overlapping area 31. The end sections 21A, 21B are configured to slide in relation to each other, and the first expandable metal sleeve 6 and the second expandable metal sleeve 8 define an annular space 15 together with the tubular metal part. The first expandable metal sleeve 6 extends from its second end away from the overlapping area in a first direction along the axial direction, and the second expandable metal sleeve 8 extends from its second end 21B away from the overlapping area in a second direction opposite the first direction.

By having an annular barrier 1 having two expandable and partly overlapping metal sleeves, an annular barrier having a larger radial expansion than known annular barriers is obtained. Known annular barriers have a metal sleeve which during expansion are thinning, and this thinning defines the maximum radial expansion since the sleeve is to withstand a predetermined collapse pressure after expansion, and thus the sleeve cannot be expanded more than being able to withstand the collapse pressure. By having the two overlapping sleeves, the sleeves slide away from each other during expansion and the thinning is minimised, and thus the annular barrier of the present invention can be expanded radially further outwards compared with annular barriers having sleeves of same material conditions and thickness.

The end section 21, 21A of the first expandable metal sleeve and the end section 21, 21B of the second expandable metal sleeve are partly overlapping along the axial direction creating an overlapping area 31 along the whole circumference of the annular barrier.

In FIG. 1A, the annular barrier is shown in its unexpanded position, and each expandable metal sleeve has a first section 41 and a second section 42. The second section is the end sections 21, 21A, 21B, and the first section is the rest of the expandable metal sleeve so that the first expandable metal sleeve 6 has a first section 41 and a second section 42 being its end section 21A, and the second expandable metal sleeve 8 has a first section 41 and a second section 42 being its end section 21B along the axial direction. In FIG. 1B, fluid from an inside 23 of the tubular metal part 7 has entered the opening 16 and further into the annular space 15, and the first section of the sleeves are expanded until abutting the wall 24 of the borehole 2.

As can be seen in FIGS. 1A and 1B, the end sections 21A, 21B of the overlapping area 31 are unconnected to the outer face 4 of the tubular metal part 7 both in the unexpanded condition shown in FIG. 1A and the expanded condition shown in FIG. 1B. Thus, the overlapping area 31 is without connection to the outer face 4 of the tubular metal part 7.

In one embodiment, the material of the expandable metal sleeves 6, 8 in the overlapping area 31 is less ductile than the rest of the expandable metal sleeves so that the first section 41 of the expandable metal sleeves expands while the second sections remain substantially unexpanded when setting the annular barrier 1.

In another embodiment, the end sections 21, 21A, 21B of the overlapping area have a greater thickness than the rest of the expandable metal sleeves so that the first section of the expandable metal sleeves expands while the second sections remain substantially unexpanded when setting the annular barrier 1. Thus, the material of the expandable metal sleeves 6, 8 in the overlapping area 31 may be hardened e.g. by thermal treatment and/or deformations hardening.

Furthermore, the material of the expandable metal sleeves 6, 8 in the overlapping area 31 may be different from the rest of the expandable metal sleeves 6, 8 and welded together so that the first sections are made of a different material than the second sections.

In FIGS. 1A and 1B, sealing elements 29 are arranged between the end sections of the overlapping area. Each sealing element 29 is arranged in a groove 30 in one of the end sections of the expandable metal sleeves. The end section 21A of the first expandable metal sleeve 6 is arranged sliding along an outer face 32 of the second expandable metal sleeve so that the end of the second expandable metal sleeve extends into the annular space 15 and during expansion provides a piston effect i.e. a pressure in the axial direction to the end of the second expandable metal sleeve. The first section has an unexpanded condition as shown in FIG. 1A and an expanded condition shown in FIG. 1B, and the first section is capable of expanding more than 30% than in the unexpanded condition.

The end section 21 of each sleeve has a length L1 of at least 5% of a total length L2 of the expandable metal sleeve in the unexpanded condition. The length of the end section of the first expandable metal sleeve may vary from the length of the end section of the second expandable metal sleeve.

FIGS. 2A-2C show the annular barrier 1 providing zonal isolation within a tubular structure 3A sealing off a first zone from a second zone. In FIG. 2A, the annular barrier is shown in its unexpanded condition which is the initial position of the annular barrier when running the well tubular metal structure into the well. The first ends 9, 12 of the expandable metal sleeves 6, 8 are welded onto the outer face 4 of the tubular metal part 7. In another embodiment, the annular barrier comprises connection parts connecting the first ends to the tubular part and in FIGS. 1A and 1B, distance rings 51 are arranged underneath the sleeves at the first ends and welded to the tubular metal part.

In FIGS. 1A-1B, the first expandable metal sleeve is casted and machined in one piece, and the second expandable metal sleeve is likewise in one piece and not mounted or welded from several pieces. Thus, the first section 41 and the second section 42 of each expandable metal sleeve are made in one piece. However, in FIGS. 2A-2C, the second section of the first expandable metal sleeve is welded to the first section of the first expandable metal sleeve by means of a connection element 52, and thus the first expandable metal sleeve is mounted and welded from three pieces. The second section of the second expandable metal sleeve is welded to the first section of the second expandable metal sleeve, and a retainer ring 53 is mounted over the connection. FIG. 2B shows the annular barrier during expansion, and FIG. 2C discloses the annular barrier fully expanded. In FIG. 2C, the connection element 52 is somewhat expanded and functions as a retainer ring like retainer ring 53 which is also slightly expanded. However, the second sections remain substantially unexpanded. After expansion, the sealing elements 28 provide the sealing capability of the annular barrier against the tubular structure 3A and the confined space 54 provided between the expanded first sections, the second sections and the tubular structure are not subjected to any substantial pressure and do not have to withstand a predetermined collapse pressure. Thus, the overlapping section does not have to withstand high pressure.

In FIG. 3, the end section of the first expandable metal sleeve has grooves 33 which correspond to grooves 34 on the outer face 32 of the end section of the second expandable metal sleeve forming a ratchet system 35 hindering the end section of the first expandable metal sleeve from returning once moved away from the end section of the second expandable metal sleeve.

In FIG. 4, the annular barrier 1 further comprises a shear pin assembly 37 fluidly connecting the opening and the annular space in order to allow expansion fluid within the well tubular structure 3 to expand the expandable metal sleeves 6, 8. The shear pin assembly 37 has a first position (shown in FIG. 5A) in which expansion fluid is allowed to flow into the annular space 15 and a second position (shown in FIG. 5B) in which the opening 16 is blocked, preventing expansion fluid from entering the annular space 15. As shown in FIG. 4, the annular barrier further comprises an anti-collapsing unit 11 comprising an element 20, such as a ball as shown in FIG. 6, movable at least between a first position and a second position, the anti-collapsing unit having a first inlet 25 which is in fluid communication with the first zone, and a second inlet 26 which is in fluid communication with the second zone, and the anti-collapsing unit having an outlet 27 which is in fluid communication with the annular space, and in the first position, the first inlet is in fluid communication with the outlet, equalising the first pressure of the first zone 101 with the space pressure in the annular space, and in the second position, the second inlet is in fluid communication with the outlet, equalising the second pressure of the second zone with the space pressure.

As shown in FIG. 4, the annular barrier 1 further comprises the shear pin assembly 37. The shear pin assembly 37 has a port A receiving fluid from an inside of the well tubular structure 3 through a screen 44. The port A is fluidly connected with a port D during expansion, causing the expansion fluid within the well tubular structure to expand the expandable sleeves 6, 8. When the expandable sleeves 6, 8 are expanded to abut the wall of the tubular structure, the pressure builds up and a shear pin or disc within the shear pin assembly shears closing the fluid connection from port A and the opening 16 (as shown in FIG. 5B) and opens the fluid connection between a port B (in fluid communication with the outlet 27) and a port C (in fluid communication with the annular space 15) so that fluid from the second inlet 26 can be let into the annular space 15 through the shear pin assembly. When the first pressure increases in the first zone, fluid from a port E connected with a port I, being the first inlet 25, presses the element 20 (shown in FIG. 6) to move so that fluid communication is provided between port I and a port H, being the outlet, and thus further through ports B and C and into the annular space through port D. When the second pressure increases in the second zone, the element is forced in the opposite direction, and fluid communication between port G (in fluid communication with the second zone through port F) and port H is provided, i.e. fluid communication between the second inlet 26 and the outlet 27 of the anti-collapsing unit 11, and thus, fluid is let into the annular space through ports B, C and D.

The shear pin assembly shown in FIG. 5A and 5B comprises a first bore part 19 having a first inner diameter and a second bore part 120 having an inner diameter which is larger than that of the first bore part. The opening 16 and a second opening 17 are arranged in the first bore part 19 and are displaced along the bore extension. The annular barrier 1 further comprises a piston 121 arranged in the bore 18, the piston comprising a first piston part 22 having an outer diameter substantially corresponding to the inner diameter of the first bore part 19 and comprising a second piston part 23B having an outer diameter substantially corresponding to the inner diameter of the second bore part 120. The annular barrier 1 further comprises a rupture element 24B preventing movement of the piston 121 until a predetermined pressure in the bore 18 is reached. The strength of the rupture element is set based on a predetermined pressure acting on the areas of the ends of the piston, and thus, the difference in outer diameters results in a movement of the piston when the pressure exceeds the predetermined pressure. The piston 121 comprises a fluid channel 125 being a through bore providing fluid communication between the first and second bore parts 19, 120.

In FIGS. 5A and 5B, the rupture element 24B is a shear pin but may also be a disc. In FIG. 5A, the shear pin is intact and extends through the piston and the inserts 43, and in FIG. 5B, the shear pin is sheared, and the piston is allowed to move, and the inserts 43 have moved towards the centre of the bore 18. Depending on the isolation solution required to provide isolation downhole, the rupture element 24B is selected based on the expansion pressure so as to break at a pressure higher than the expansion pressure but lower than the pressure rupturing the expandable metal sleeve or jeopardising the function of other completion components downhole. The bore 18 and the piston 121 may be arranged in a connection part connecting the first ends to the tubular metal part.

In FIG. 5A, the annular barrier 1 comprises a locking element 38 which is arranged around the second piston part 23B. The bore further comprises a third opening 137 in the second bore part 120, which third opening is in fluid communication with the annular space 15 and the annulus/borehole 2. The third opening 137 may be arranged in fluid communication with a shuttle valve (i.e. the anti-collapsing unit 11), as shown in FIG. 6, in such a way that the shuttle valve is arranged between the third opening and the annulus, thus providing fluid communication between the annular space and the annulus. The shuttle valve provides, in a first position, fluid communication between the annular space and the first zone 101 of the annulus (shown in FIG. 1B), and in a second position, the shuttle valve provides fluid communication between the annular space and the second zone 102 of the annulus (shown in FIG. 1B).

As shown in FIG. 1A, the annular barrier further comprises sealing elements 28 arranged on an outer face 32, 36 of the expandable metal sleeves. The sealing elements 28 may be arranged in grooves 48 on the outer face of the expandable metal sleeves. Split ring-shaped retaining elements 47 are arranged between the first and second circumferential edges in the groove 48, and the split ring-shaped retaining elements form a back-up for the sealing element. Each split ring-shaped retaining element 47 has more than one winding so that when the expandable metal sleeves are expanded from a first outer diameter to a second outer diameter being larger than the first outer diameter, the split ring-shaped retaining element 47 partly unwinds. An intermediate element 49 is arranged between the split ring-shaped retaining element 47 and the sealing element 28. In FIG. 1A, the grooves are provided between two projections 50.

As shown in FIGS. 5A and 5B, the annular barrier 1 further comprises a first connection part (not shown) connecting the first end of the first expandable metal sleeve to the outer face of the tubular metal part and a second connection part connecting 45 the first end of the second expandable metal sleeve to the outer face of the tubular metal part.

In FIG. 7, a cross-sectional view of another annular barrier in its unexpanded condition is shown. The annular barrier comprises two connecting rings 56, one connecting ring 56 connects the first end 9 of the first expandable metal sleeve 6 and the other connecting ring 56 connects the first end 12 of the second expandable metal sleeve 8. The connecting rings 56 overlap the first ends and decrease the free expansion of the first ends. The connecting rings 56 are welded to the tubular metal part 7 and the connecting rings 56 are also welded to the expandable metal sleeves. Each expandable metal sleeve has a first section 41 and a second section 42. The second section is the end sections 21, 21A, 21B and the first section is the rest of the expandable metal sleeve. In FIG. 7, the second section 42 of the first expandable metal sleeve 6 is the inner most second section in the overlapping area 31, and in FIG. 1A, the second section 42 of the first expandable metal sleeve 6 is the outer most second section in the overlapping area 31.

As shown in FIG. 8, the annular barrier comprises a third expandable metal sleeve 55 surrounding the tubular metal part. The third expandable metal sleeve has a first end 56 connected with the outer face of the tubular metal part and a second end (57) facing the second expandable metal sleeve so that an end section 58 of the first end 12 of the second expandable metal sleeve 8 and an end section 59 of the second end of the third expandable metal sleeve are partly overlapping along the axial direction creating a second overlapping area 31B. Thus, the second expandable metal sleeve is arranged intermediate the first expandable metal sleeve and the third expandable metal sleeve, so that the end sections of the second expandable metal sleeve partly overlap the first and the third expandable metal sleeves, and so that the first, the second and third expandable metal sleeves are arranged in succession but partly overlapping along the axial direction creating one common sleeve. One end of the first expandable metal sleeve is connected to the tubular metal part and the other end slidably connected to the second expandable metal sleeve. One end of the third expandable metal sleeve is connected to the tubular metal part and the other end slidably connected to the second expandable metal sleeve. The second expandable metal sleeve is thus connected with the tubular metal part via the first and third expandable metal sleeves and the inner face of at least the ends of the second expandable metal sleeve is in its unexpanded condition abutting the outer face of the tubular metal part. The end section 59 of the second end of the third expandable metal sleeve is overlapping the end section 58 of the first end 12 of the second expandable metal sleeve 8, and the end section of the second end 10 of the first expandable metal sleeve 6 is overlapping the end section of the second end 14 of the second expandable metal sleeve 8. The second expandable metal sleeve is thus maintained in place by the overlapping ends of the first and third expandable metal sleeves during insertion of the annular barrier into the well. During expansion of the annular barrier, the second expandable metal sleeve is radially expanding along with the overlapping ends of the first and third expandable metal sleeves. The ends of the second expandable metal sleeve slide in relation to the end of the first expandable metal sleeve and the end of the third expandable metal sleeve during expansion. During radial expansion of the second expandable metal sleeve, the second expandable metal sleeve is not prohibited in decreasing in length since the second expandable metal sleeve is not fastened to the tubular metal part, and thus the thinning of the second expandable metal sleeve is less than if one end of the second expandable metal sleeve were fastened to the tubular metal part since that end would experience more thinning.

The end section 21, 21A of the first expandable metal sleeve and the end section 21, 21B of the second expandable metal sleeve are partly overlapping along the axial direction creating an overlapping area 31 along the whole circumference of the annular barrier. In the same way, the end section 59 of the third expandable metal sleeve and the end section 58 of the second expandable metal sleeve are partly overlapping along the axial direction creating an overlapping area 31B along the whole circumference of the annular barrier.

The end section of the second end 14 of the second expandable metal sleeve is arranged sliding along an inner face 61 of the first expandable metal sleeve and the end section of the first end 12 of the second expandable metal sleeve is arranged sliding along an inner face 62 of the third expandable metal sleeve. Sealing elements are provided in the outer face of the second expandable metal sleeve so as to seal against the inner face 61 and 62. Thus, the annular barrier of FIG. 8 has two overlapping areas 31 and 31B with sealing elements therebetween. The annular space 15 is defined by the first, the second and the third expandable metal sleeves and the tubular metal part 7.

As can be seen in FIG. 8, the second end 10 of the first expandable metal sleeve 6 and the second end 57 of the third expandable metal sleeve are decreasing in thickness towards its ends so as to have the greatest thickness opposite the sealing elements in the outer face of the second expandable metal sleeve in its unexpanded condition as shown in FIG. 8. The end sections of the overlapping areas have a greater common thickness than the rest of the second expandable metal sleeve.

The second expandable metal sleeve has a slightly small thickness intermediate its first and second ends when seen in cross-section along the axial direction of the annular barrier so that the expansion initially occurs at the intermediate part of the second expandable metal sleeve not overlapping the ends of the first and third expandable metal sleeves.

The first end of the first expandable metal sleeve and the first end of the third expandable metal sleeve are fastened to the tubular metal part e.g. by means of welding or similar fastening. One of the first ends of the first expandable metal sleeve and the first end of the third expandable metal sleeve may also be slidably connected to the tubular metal part.

The annular barrier may be expanded by pressurising the well tubular metal structure from surface or pressurising the well tubular metal structure from surface by means of drill pipe connecting the well tubular metal structure to surface. The annular barrier may also be expanded by means of a tool isolating a section opposite the opening 16.

By fluid or well fluid is meant any kind of fluid that may be present in oil or gas wells downhole, such as natural gas, oil, oil mud, crude oil, water etc. By gas is meant any kind of gas composition present in a well, completion or open hole, and by oil is meant any kind of oil composition, such as crude oil, an oil-containing fluid etc. Gas, oil and water fluids may thus all comprise other elements or substances than gas, oil and/or water, respectively.

By a casing, tubular structure or well tubular metal structure is meant any kind of pipe, tubing, tubular, liner, string etc. used downhole in relation to oil or natural gas production.

In the event that the tool is not submergible all the way into the casing, a downhole tractor can be used to push the tool all the way into position in the well. The downhole tractor may have projectable arms having wheels, wherein the wheels contact the inner surface of the casing for propelling the tractor and the tool forwards in the casing. A downhole tractor is any kind of driving tool capable of pushing or pulling tools in a well downhole, such as a Well Tractor®.

Although the invention has been described in the above in connection with preferred embodiments of the invention, it will be evident for a person skilled in the art that several modifications are conceivable without departing from the invention as defined by the following claims. 

1. An annular barrier for providing zonal isolation within a tubular structure or a borehole and for sealing off a first zone from a second zone, comprising: tubular metal part configured to be mounted as part of a well tubular metal structure, the tubular metal part having an outer face, an opening and an axial direction along the well tubular metal structure, a first expandable metal sleeve surrounding the tubular metal part and having a first end connected with the outer face of the tubular metal part and a second end, a second expandable metal sleeve surrounding the tubular metal part and having a first end connected with the outer face of the tubular metal part and a second end, and an annular space between the tubular metal part and the expandable metal sleeves, wherein the first expandable metal sleeve and the second expandable metal sleeve each have an end section at the second end, the end section of the first expandable metal sleeve and the end section of the second expandable metal sleeve are at least partly overlapping along the axial direction creating an overlapping area, the end sections are configured to slide in relation to each other, the first expandable metal sleeve extends from the second end of the first expandable metal sleeve away from the overlapping area in a first direction along the axial direction, and the second expandable metal sleeve extends from the second end of the second expandable metal sleeve away from the overlapping area in a second direction opposite the first direction.
 2. An annular barrier according to claim 1, wherein the end sections of the overlapping area are unconnected to the outer face of the tubular metal part.
 3. An annular barrier according to claim 1, further comprising a third expandable metal sleeve surrounding the tubular metal part and having a first end connected with the outer face of the tubular metal part and a second end, an end section of the first end of the second expandable metal sleeve and an end section of the second end of the third expandable metal sleeve are at least partly overlapping along the axial direction creating an second overlapping area.
 4. An annular barrier according to claim 1, wherein the end sections of the overlapping area have a greater common thickness than the rest of the expandable metal sleeves.
 5. An annular barrier according to claim 1, wherein at least one sealing element is arranged between the end sections of the overlapping area(s).
 6. An annular barrier according to claim 1, wherein the end section of the first expandable metal sleeve is arranged sliding along an outer face of the second expandable metal sleeve, the end of the second sleeve provides a piston effect during expansion providing a pressure in the axial direction to the end of the second expandable metal sleeve.
 7. An annular barrier according to claim 1, wherein the end section of the second end of the second expandable metal sleeve is arranged sliding along an inner face of the first expandable metal sleeve and the end section of the first end of the second expandable metal sleeve is arranged sliding along an inner face of the third expandable metal sleeve.
 8. An annular barrier according to claim 1, wherein the overlapping area(s) remains substantially unexpanded during expansion of the rest of the expandable metal sleeve.
 9. An annular barrier according to claim 1, wherein each expandable metal sleeve is constituted by a first section and a second section, the second section is the end section.
 10. An annular barrier according to claim 8, wherein the first section has an unexpanded condition and an expanded condition, the first section is capable of expanding more than 30% than in the unexpanded condition.
 11. An annular barrier according to claim 1, wherein the end section of each sleeve has a length of at least 5% of a total length of the expandable metal sleeve in the unexpanded condition.
 12. An annular barrier according to claim 1, wherein the end section of the first expandable metal sleeve has grooves which correspond to grooves on the outer face of the end section of the second expandable metal sleeve forming a ratchet system hindering the end section of the first expandable metal sleeve from returning once moved away from the end section of the second expandable metal sleeve.
 13. An annular barrier according to claim 1, further comprising a shear pin assembly fluidly connecting the expansion opening and the annular space in order to allow expansion fluid within the well tubular structure to expand the expandable sleeve.
 14. An annular barrier according to claim 1, further comprising an anti-collapsing unit comprising an element, such as a ball, movable at least between a first position and a second position, the anti-collapsing unit having a first inlet which is in fluid communication with the first zone, and a second inlet which is in fluid communication with the second zone, and the anti-collapsing unit having an outlet which is in fluid communication with the annular space, and in the first position, the first inlet is in fluid communication with the outlet, equalising the first pressure of the first zone with the space pressure, and in the second position, the second inlet is in fluid communication with the outlet, equalising the second pressure of the second zone with the space pressure.
 15. An annular barrier according to claim 1, further comprising sealing elements arranged on an outer face of the expandable metal sleeves.
 16. An annular barrier according to claim 1, wherein the first ends of the expandable metal sleeves are welded to the outer face of the tubular metal part. 